U.S. patent number 3,975,089 [Application Number 05/462,366] was granted by the patent office on 1976-08-17 for zoom lens.
This patent grant is currently assigned to Ponder & Best, Inc.. Invention is credited to Ellis I. Betensky.
United States Patent |
3,975,089 |
Betensky |
August 17, 1976 |
**Please see images for:
( Certificate of Correction ) ** |
Zoom lens
Abstract
A lens having an equivalent focal length variable between
predetermined limits where the lower limit is less than the
diagonal of the image frame and where the lens comprises four lens
groups of positive, negative, negative and positive powers,
respectively, and the first three groups mounted from the object
end are movable in unequal relationship to vary the focal length
while all four groups are axially movable in fixed relation to each
other to focus the lens.
Inventors: |
Betensky; Ellis I. (Toronto,
CA) |
Assignee: |
Ponder & Best, Inc. (Santa
Monica, CA)
|
Family
ID: |
23836178 |
Appl.
No.: |
05/462,366 |
Filed: |
April 19, 1974 |
Current U.S.
Class: |
359/688 |
Current CPC
Class: |
G02B
15/144109 (20190801) |
Current International
Class: |
G02B
15/17 (20060101); G02B 15/163 (20060101); G02B
015/18 () |
Field of
Search: |
;350/184,186,176,177,222,187 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sacher; Paul A.
Attorney, Agent or Firm: DeLio and Montgomery
Claims
What is claimed is:
1. A lens having an equivalent focal length variable between
predetermined limits, comprising from the object end a first
positive group, a second negative group, a third negative group,
and a fourth positive group, said first, second and third groups
being simultaneously axially movable at different rates with
respect to said fourth group to vary the focal length of said lens,
all of said lens groups being movable in axially fixed relation to
each other to vary the focus of said lens, said lens having a back
focal length greater than the equivalent focal length of said lens
over a portion of its variable focal length range.
2. The lens of claim 1 wherein the radii on which the facing
surfaces of said second and third groups are defined are
substantially one-half of the lower limit equivalent focal length
of said lens, and said surfaces are concave.
3. The lens of claim 1 wherein said second lens group has an object
side surface defined by the radius R.sub.1 and said third lens
group has an image side surface defined by the radius R.sub.2,
and
where
4. The lens of claim 3 wherein
where FL.sub.m is the geometric mean of the upper and lower focal
length limits.
5. The lens of claim 1 wherein the lower limit focal length of said
lens is between 0.8 and 0.9 of the diagonal of the image frame for
said lens.
6. The lens of claim 1 wherein the upper limit focal length of said
lens is three times or less than the lower limit focal length.
7. The lens of claim 1 defined by substantially the following
data:
Where L1--L12 are lens elements from the object end to the image
end, R1--R21 are the radii of lens elements L1--L12, N.sub.d is the
index of refraction and V.sub.d is the Abbe number.
8. A lens substantially as defined below having a variable
equivalent focal length:
Where L1-L12 are lens elements from the object end to the image
end, R1-R21 are the radii of lens elements L1-L12, N.sub.d is the
index of refraction and V.sub.d is the Abbe number.
9. A lens having an equivalent focal length variable between
predetermined limits, comprising from the object end a first
positive group, a second negative group, a third negative group,
and a fourth positive group, said first, second and third groups
being simultaneously axially movable at different rates with
respect to said fourth group to vary the focal length of said lens,
all of said lens groups being movable in axially fixed relation to
each other to vary the focus of said lens, the lower limit focal
length of said lens being 0.8 to 0.9 of the diagonal of the image
frame for said lens.
10. The lens of claim 9 wherein the radii on which the facing
surfaces of said second and third groups are defined are
substantially one-half of the lower limit equivalent focal length
of said lens, and said surfaces are concave.
11. The lens of claim 9 wherein said second lens group has an
object side surface defined by the radius R.sub.1 and said third
lens group has an image side surface defined by the radius R.sub.2,
and
where
12. The lens of claim 11 wherein
where FL.sub.m is the geometric mean of the upper and lower focal
length limits.
13. A lens having an equivalent focal length variable between
predetermined limits, comprising from the object end a first
positive group, a second negative group, a third negative group,
and a fourth positive group, said first, second and third groups
being simultaneously axially movable at different rates with
respect to said fourth group to vary the focal length of said lens,
all of said lens groups being movable in axially fixed relation to
each other to vary the focus of said lens, the lower limit focal
length of said lens being 0.8 to 0.9 of the diagonal of the film
plane for said lens and the higher limit focal length being less
than 3.0 times the lower limit focal length.
14. The lens of claim 13 wherein the radii on which the facing
surfaces of said second and third groups are defined are
substantially one-half of the lower limit equivalent focal length
of said lens, and said surfaces are concave.
15. The lens of claim 13 wherein said second lens group has an
object side surface defined by the radius R.sub.1 and said third
lens group has an image side surface defined by the radius R.sub.2,
and
where
16. The lens of claim 15 wherein
where FL.sub.m is the geometric mean of the upper and lower focal
length limits.
17. The lens of claim 13 defined by substantially the following
data:
Where L1-L12 are lens elements from the object end to the image
end, R1-R21 are the radii of lens elements L1-L12, N.sub.d is the
index of refraction and V.sub.d is the Abbe number.
18. A lens having an equivalent focal length variable between
predetermined limits, comprising from the object end a first
positive group, a second negative group, a third negative group,
and a fourth positive group, said first, second and third groups
being simultaneously axially movable at different rates with
respect to said fourth group to vary the focal length of said lens,
all of said lens groups being movable in axially fixed relation to
each other to vary the focus of said lens, said lens having a back
focal length greater than the equivalent focal length of said lens
over a portion of its variable focal length range, said second and
third groups having facing concave surfaces.
19. The lens of claim 18 wherein said second lens group has an
object side surface defined by the radius R.sub.1 and said third
lens group has an image side surface defined by the radius R.sub.2,
and
where
and
where FL.sub.m is the geometric mean of the upper and lower focal
length limits.
Description
This invention relates to lenses and more particularly relates to
variable focal length or zoom lenses.
Zoom lenses conventionally comprise four major lens groups where
from the object end the first group is utilized for focusing, the
second and third groups are moved to vary the focal length and
compensate for image position with the change and the fourth lens
group is stationary.
The motions of the second and third groups are unequal with respect
to each other. Therefore it is necessary to select powers of the
lens groups so as to provide the necessary motions of the second
and third groups within the allowable space.
In lenses of the type described, it is necessary to choose the lens
powers in such a manner as to provide sufficient space to
accomplish the desired zooming. Dependent on the zoom range
desired, this can increase the front vertex distance (FVD) of the
lens. A significantly improved zoom lens which is much more compact
could be provided if the moving lens groups could pass through or
intersect each other. This, of course, cannot be accomplished
physically.
However, in the present invention the same effect is achieved with
a virtual image for the second group derived by moving the first
lens to provide a virtual object in the appropriate location. The
present invention provides a more compact zoom lens having a lower
section of its focal length range less than the image frame
diagonal by imparting predetermined motion to the front element
during zooming of the second and third groups.
The movement of the first group during zooming further enhances the
lens design by providing a greater opportunity to introduce the
proper compensating changes in aberration to correct the zoom lens
over the entire range. This is particularly true in zoom lenses
that will zoom to a wide angle EFL. Here as the field angles
increase with decreasing EFL, the change of astigmatism and
variations of coma become significantly greater. Conventional
two-moving lens group zoom lenses operating in the wide angle
equivalent focal length range do not provide the opportunity to
entirely correct and compensate for these aberrations.
Accordingly, the present invention provides a new and improved zoom
lens where the shortest EFL is such that the lens may be termed a
wide angle lens. Otherwise stated, a lens embodying the invention
will have its shortest EFL a smaller dimension than the diagonal of
the image frame, and in some focal lengths the lens becomes
retrofocus.
Briefly stated, the invention in one form thereof comprises a
four-lens group zoom lens where the first lens group from the
object side is of positive power. The second and third lens groups
are of negative power and the fourth lens group is of positive
power. The lens groups are arranged so that all four groups move in
fixed relation during focusing, and the first, second and third
groups move in predetermined unequal relation with respect to each
other during zooming. The second and third groups have a particular
range of lens radii parameters in order to simultaneously correct
for astigmatism, coma and distortion as the first group moves to
vary the focal length, which parameters are hereinafter
described.
An object of this invention is to provide a new and improved
compact zoom lens.
Another object of this invention is to provide a compact zoom lens
having fifteen percent of its focal length range in the wide angle
range and extending into the telephoto range.
Another object of this invention is to provide a lens of the type
described having a large relative aperture.
The features of the invention which are believed to be novel are
particularly pointed out and distinctly claimed in the concluding
portion of this specification. However, the invention together with
further objects and advantages thereof may best be appreciated by
reference to the following detailed description taken in
conjunction with the drawing, wherein:
FIG. 1 is a diagrammatic view of a lens embodying the
invention;
FIG. 2 is a plot of the movements of the zooming lens groups with
respect to focal length;
FIG. 3 is a side elevation in half section of a lens housing
structure in which the lens may be mounted; and
FIG. 4 is a plane developed view of annular members of the
structure of FIG. 3 set forth to facilitate explanation of the
movements.
A lens embodying the invention comprises a twelve-element lens
L1-L12 arranged in four groups. The surface radii of each element
is denoted by R1-R21 as shown in FIG. 1. The groups comprise the
elements as shown below:
GROUP I Elements L1, L2, L3 GROUP II Elements L4 and L5 GROUP III
Elements L6 and L7 GROUP IV Elements L8 - L12.
Group I is of converging or positive power. Group II is of negative
or diverging power. Group III is of negative or diverging power and
Group IV is of positive or converging power.
Element L1 is a meniscus with a concave side toward the image
plane. Element L2 is bi-convex. Element L3 is convex-concave.
Element L4 is bi-convex and cemented to element L5 which is
bi-concave. Elements L6 and L7 comprise a cemented doublet with L6
being bi-concave and element L7 bi-convex. Element L8 is bi-convex.
Element L9 is bi-convex and cemented to the concave surface of
meniscus L9. Element L11 is bi-convex and element L12 is a meniscus
with the convex side facing the image plane.
The lens of FIG. 1 as scaled to a 36-83mm focal length for a
36.times.24mm image frame and a relative aperture of f/2.8 may be
further defined by the data of Table I below:
TABLE I ______________________________________ Axial Distance
Surface Between Radius Surfaces Lens (mm) (mm) N.sub.d V.sub.d
______________________________________ R1 135.72 L1 2.60 1.805 25.5
R2 46.71 2.84 R3 46.50 L2 13.80 1.531 62.1 R4 -152.15 0.100 R5
41.84 L3 6.60 1.694 53.3 R6 125.20 (1) R7 140.19 L4 3.10 1.847 23.8
R8 - 60.45 L5 1.10 1.834 37.3 R9 17.98 (2) R10 - 16.56 L6 1.00
1.498 65.1 R11 22.97 L7 3.10 1.785 25.7 R12 -112.11 (3) R13 53.32
L8 2.90 1.620 60.3 R14 - 42.06 2.00 R15 -502.33 L9 5.00 1.487 70.4
R16 - 14.89 L10 0.90 1.805 25.5 R17 - 45.59 11.53 R18 125.96 L11
3.50 1.639 45.1 R19 - 25.90 5.98 R20 - 19.40 L12 1.296 1.805 25.5
R21 - 35.59 ______________________________________ (1) .47 - 19.48
(2) 15.94 - 5.01 (3) 9.33 - 1.19
Where N.sub.d is the index of refraction, V.sub.d is the Abbe
number, L1-L12 are lens elements from the object end, and R1-R21
are the radii of lens surfaces, and the distances between radii are
measured on the axis of the lens.
During a zooming mode of operation from the longer equivalent focal
length EFL to the shorter EFL, Groups II and III will move towards
the object at unequal rates and Group I will initially move toward
the object and then back toward the image. Plots of movement of
lens Groups I, II and III during a zooming mode of operation are
set forth in FIG. 2 in which the abscissa is equivalent focal
length and the ordinant is in millimeters as measured from the
axial point on the object side of the surface of lens L8. All
movements are taken with respect to the axial center point of lens
surface R13. The particular lens disclosed has an equivalent focal
length range of 36-83mm and a relative aperture of f/2.8.
A lens embodying the invention with a positive front or first group
may have a lower limit equivalent focal length of about 0.8 to 0.9
of the diagonal of the image frame. In the foregoing example the
diagonal of the 24 .times. 36 mm image frame is 43.27 mm. The upper
limit focal length is not critical but for practical purposes will
be about three times or less than the lower limit.
The movement of Groups I, II and III may be accomplished through a
lens 30 as shown in FIG. 3. Reference is also made to FIG. 4 to
enhance explanation of the lens movements. The lens 30 comprises a
primary body member 31, having a camera mounting portion 32, shown
as being of the screw type. A tubular lens mounting member 33
extends at least partially into body member 32, and has an
externally threaded rear portion 34, and an axially directed slot
35 therein. A focusing member 36 has internal threads 37 engaging
threads 34. A pin 38 carried in body member 31 extends into lens
mounting slot. Thus when focusing member 36 is rotated, it imparts
only linear movement to lens mounting member 33. A pin 39 is
carried in body member 31 and extends into an annular slot 40
defined in focusing member 36. Focusing member 36 has one or more
axially extending arms 41, which may be defined on a portion of a
spiral for reasons hereinafter made apparent. At least one arm 41
carries a pin 42 therein which extends into an axial slot 43 in a
focus and zoom operating member 44.
A Group I lens mount 45 includes a tubular portion 46
telescopically extending over lens mounting member 33. A Group II
lens mount 47 includes a tubular portion 48 within lens mounting
member 33. A Group III mount 49 includes a tubular portion 50
within tubular portion 48. In FIG. 3 the lens groups I, II, III and
IV are shown as single elements for simplicity of illustration.
Group IV is set in a mount 51 fixed in lens mounting member 33. The
tubular or sleeve-like portions 46 and 50 are close fitting but
easily slidable with respect to tube portion 33a of mounting 33.
Portion 50 is close fitting but slides easily in portion 48.
Reference is now made to FIG. 4 in conjunction with FIG. 3. FIG. 4
shows tubular members 33a, 46, 48 and 50 developed into planar
members. Tube 33a has a plurality of cam slots therein which define
the movements of mounts 45, 47 and 49. Pins 52 from mount 47 extend
through cam slots 53 and tube 33a, and axial slots 54 in tube 46,
to a ring member 55 (FIG. 3). Pins 56 extend from ring member 55 to
slots 57 in control member 44. The slots 57 are defined on a pitch
equivalent to the pitch of threads 34 and 37 for reasons
hereinafter made apparent.
As thus far described, as control member 44 is moved axially along
the lens, pins 52 will move in cam slots 53, and mount 47 will move
both axially and rotatably along tube 33a.
Tube 48 has axial slots 58 and 59 defined therein. A pin 60 carried
by mount 49 extends through slot 58 into a cam slot 61 in tube 33a.
A pin 62 extends into slot 59 through a cam slot 63 in tube 33a.
The edges defining the slots 58 and 59, upon rotative motion of
mount 47 imparts rotative motion to tubes 50 and 46, respectively,
through pins 62 and 60, respectively. The rotative motion imparted
to pins 60 and 62 causes them and their respective lens mounts to
follow the cam slots 61 and 63, respectively, and predetermine the
relative motions of lens Group I, II, and III, as shown in FIG.
2.
For focusing, control member 44 is rotated. This produces rotation
of focusing member 36, and linear movement of lens mounting member
33 with all lens groups in fixed relation to one another. The
linear motion of mounting member 33 corresponds with the pitch of
slots 57 and no zooming effect is imparted to the lens groups. The
operator may zoom and focus simultaneously with the control member
44.
The lens mechanical means for producing the desired motions is set
forth in more detail in the copending application of Masatoshi
Shimojima Ser. No. 462,300 filed on the same day as this
application, now U.S. Pat. No. 3,915,557.
The movement of Group I during zooming permits a more compact lens
design by decreasing the otherwise required movements of Groups II
and III. Otherwise stated, the movement of Group I optically
increases the effective range of movement of Groups II and III
without increasing the physical dimensional movement. The movement
of Group I during zooming further permits optical corrections
otherwise not available in two moving group zoom lenses.
Table II exemplifies the extent of movement of lens groups I, II
and III when moved to vary the focal length of the lens from 83mm
to 36mm as the groups move toward or away from the object between
the upper and lower equivalent focal length limits.
TABLE II ______________________________________ Group I 3.24mm
(decreasing EFL) 3.15mm (increasing EFL) Group II 19.07mm Group III
8.14mm ______________________________________
The foregoing table exemplifies the relatively short travel,
particularly of group II, to vary the equivalent focal length of
the lens. Only a small degree of movement of the first positive
group is required to substantially reduce the travel of group II
and provide a very compact lens for the range of equivalent focal
lengths. This, in turn, enables the powers of the lens groups to be
reduced with resulting benefit in optical properties. The powers of
the lens groups are given in Table III.
TABLE III ______________________________________ Group I .0157
Group II -.0395 Group III -.0098 Group IV .0333 Groups I, II, III
-.0301 Groups I, II, III, IV .0277
______________________________________
The last two powers given are at an equivalent focal length of
36mm.
The front vertex distance of the lens is 133.7mm at the lower end
of the focal length range and 135.7mm at the higher end of the
focal length range.
The lens thus may vary from a wide angle focal length where it is a
retrofocus lens to a 2.3 focal length zooming ratio and has a front
vertex distance of only 1.63 times the maximum focal length.
The back focal length of the lens is 40.06mm. This is greater than
the equivalent focal length through over 8 percent of the focal
length range.
To exemplify the advantages desired from a lens embodying the
invention, a lens of the same overall dimension was computed having
the same first order properties, but with only groups II and III
movable for zooming. The powers of the lens groups were
TABLE IV ______________________________________ Group I .0159 Group
II -.0388 Group III -.0178 Group IV .0371
______________________________________
The second and third lens groups of the above-identified lens had
essentially the same motion as the corresponding groups of the lens
groups of Tables I and III. However, the power of group III
increased over 80 percent. It is apparent that if the powers were
held the same, the movement of lens groups II and III would have to
be greater and the front vertex distance increased to permit such
movement.
In the design of wide angle lens, (where the EFL of the lens is
less than the diagonal of the image frame) the limiting aberration
is higher order field curvature. This aberration measured laterally
changes from 0.088 in the lens of Tables I and II to 0.1 for the
two moving group lens of Table IV.
In order to maintain the lateral aberration acceptably small for an
intended film application, a third order field curvature must be
introduced. It is well known to those skilled in the art that the
increased third order field curvature, known as Petzval sum, will
result in poor performance due to the out-of-focus condition for
off-axis field points. Additionally, aberrations are largely
dependent upon lens powers. For example, the third order spherical
aberration varies as the cube of the power. Since it is necessary
to correct the third order aberrations introduced by one lens
element with cancelling aberrations introduced by other elements
the importance of maintaining minimum lens powers is apparent.
To achieve the compact wide angle to telephoto zoom lens in
accordance with the invention which utilizes three moving elements
to reduce the front vertex distance certain relationships of
elements are desired.
More specifically, the following relationship should be achieved
for the facing surfaces R9 and R10 of the second and third lens
groups.
Where R is the radius of surfaces R9 or R10 and EFL.sub.s is the
shortest equivalent focal length of the lens.
Additionally, it is preferred that the following relationship be
maintained.
where
where R.sub.1 is the radius of the object side surface of the
second lens group, corresponding to R7 of FIG. 1 and Table I, and
R.sub.2 is the radius of the image side of the third group,
corresponding to R.sub.12 of FIG. 1 and Table I.
A further desired parameter of the disclosed lens for the focal
length range mentioned is that
where FL.sub.m is the geometrical mean of the extremes of the focal
length range, that is the square root of the product of the extreme
focal lengths.
Where a lens is designed in accordance with these parameters, the
FVD is kept to a minimum yielding a compact wide-angle to telephoto
zoom lens, and aberrations are reduced to an extent heretofore
unachieved in a wide angle to telephoto zoom lens.
It may thus be seen that the objects of the invention set forth as
well as those made apparent from the foregoing description are
efficiently attained. While preferred embodiments of the invention
have been set forth for purposes of disclosure, modification to the
disclosed embodiments of the invention as well as other embodiments
thereof may occur to those skilled in the art. Accordingly, the
appended claims are intended to cover all embodiments of the
invention and modifications to the disclosed embodiments which do
not depart from the spirit and scope of the invention.
* * * * *